1. Field of the Invention
The present invention generally relates to transistor and capacitor fabrication from nanotube formations.
2. Background
Traditional field effect transistors (FET's), capacitors, and other electrical devices are familiar conventional devices commonly incorporated as a fundamental building block into many integrated circuit (IC) chips.
FET's operate by providing resistance in a channel region separating a source and a drain. Carriers flow from the source to the drain through the channel in proportion to the variation in electrical resistivity. Electrons are responsible for channel conduction in n-channel FET's and, in p-channel FET's, holes are responsible for conduction in the channel.
FET's can be classified into horizontal architectures and vertical architectures. Horizontal FET's exhibit carrier flow from source to drain in a direction parallel to the horizontal plane of the substrate on which they are formed. Vertical FET's exhibit carrier flow from source to drain in a direction vertical to the horizontal plane of the substrate on which they are formed.
It is commonly understood that vertical FET's provide and/or allow for a shorter switching time because channel length for vertical FET's does not depend on the smallest feature size resolvable by, for example, lithographic equipment and methods. Therefore, vertical FET's possess a higher power handling capacity than typical horizontal FET's.
To improve speed, a push has resulted in the downward scaling of FET dimensions. This downward scaling has improved performance and increased the functional capability of FET's packed on an IC chip. However, traditional materials of construction for FET's cannot be reduced much more with current manufacturing methods. Accordingly, there was a need for a new material from which to manufacture FET's, i.e., nanotubes, such as carbon nanotubes.
Batteries, capacitors, and supercapacitors are types of energy storage devices. In measuring performance, typical characteristics of measurement comprise the devices energy density, the amount of energy that can be stored per unit weight or volume, and power density, the rate at which an amount of energy can be transferred in or out of that unit weight or volume.
Batteries are common energy storage devices for providing portable power. Capacitors are also common energy storage devices. Although capacitors have much higher energy transfer rates than batteries and can withstand orders of magnitude more charging cycles, they are limited by their low energy storage capacity. Supercapacitors, also known as ultracapacitors, electrochemical capacitors or electrical double-layer capacitors, are energy storage devices which combine the high energy storage potential of batteries with the high energy transfer rate and high recharging capabilities of capacitors. However, as with FET's, the art field desires to further decrease the size and/or improve the operating characteristics of these devices.
Carbon nanotubes are nanoscale high-aspect-ratio cylinders consisting of hexagonal rings of carbon atoms that may assume either a semiconducting electronic state or a conducting electronic state. Semiconducting carbon nanotubes have been used to form hybrid devices, such as hybrid FET's. In particular, FET's have been fabricated using a single semiconducting carbon nanotube as a channel region. Typically, ohmic contacts at opposite ends of the semiconducting carbon nanotube extending between a source electrode and a drain electrode situated on the surface of a substrate.
A gate electrode is defined in the substrate underlying the carbon nanotube and generally between the source and drain electrodes. An oxidized surface of the substrate defines a gate dielectric situated between the buried gate electrode and the carbon nanotube. Such FET's switch reliably while consuming significantly less power than a comparable silicon-based device structure due to the small dimensions of the carbon nanotube.
Accordingly, much attention has been given to the use nanomaterials in electrical devices.
Carbon nanotubes are nanoscale high-aspect-ratio cylinders consisting of hexagonal rings of carbon atoms that may assume either a semiconducting electronic state or a conducting electronic state. Many methods exist for forming and/or creating nanotubes and nanotube arrays. A conventional method of forming carbon nanotubes utilizes a chemical vapor deposition (CVD) process. Specifically, the CVD process directs a flow of a carbonaceous reactant to a catalyst material located on the substrate, where the reactant is catalyzed to synthesize carbon nanotubes. The carbon nanotubes are capable of being lengthened by insertion of activated carbon atoms at the interface with the catalyst material. Typically, the carbon nanotubes are then collected for an end use or further processing.
Carbon nanotubes typically range from a few to tens of nm in diameter, and are as long as a few nanometers in length. Because of its one-dimensional electronic properties due to this shape anisotropy, the carbon nanotube characteristically has a maximum current density allowing the flowing of current without disconnection of 1,000,000 A per square centimeter, which is 100 times or more as high as that of a copper interconnect. Further, with respect to heat conduction, the carbon nanotube is ten times as high in conductivity as copper.
In terms of electric resistance, it has been reported that transportation without scattering due to impurities or lattice vibration (phonon) can be realized with respect to electrons flowing through the carbon nanotube. It is known that resistance per carbon nanotube, in various instances, is approximately 6.45 kΩ. However, other resistances are contemplated in various embodiments of the present invention.
Further desirable attributes of a carbon nanotube electrode material include such factors as high surface area for the accumulation of charge at the electrode/electrolyte interface, good intra- and interparticle conductivity in the porous matrices, good electrolyte accessibility to the intrapore surface area, chemical stability and high electrical conductivity. Commonly used carbonaceous material used for the construction of carbon nanotubes include such materials as activated carbon, carbon black, carbon fiber cloth, highly oriented pyrolytic graphite, graphite powder, graphite cloth, glassy carbon, carbon aerogel, and/or the like.
Accordingly, the art field is in search of improved methods of manufacturing electrical devices out of nanotube material, such as carbon nanotubes.